Step 1 Cook the bacon in a skillet over medium-low heat, rendering the fat. Strain the bacon fat into a measuring cup and, if you are hungry, eat the bacon. Add enough oil to the bacon fat to make two-thirds cup.
Step 2 In a blender, blend the mustard, vinegar and salt. With the blender running, slowly pour in the fat. It will create a thick emulsion. Scrape down the sides of the blender container and pulse again to combine. Set aside until ready to use. This vinaigrette can be refrigerated in a small, tightly covered jar for several days, but it will solidify. Before using, warm it gently to return it to a liquid state and shake it very well to re-emulsify.